The tires of an automobile that has been parked for a period of time form flat spots where they come into contact with the hard surface on which the automobile is parked. Later, when the automobile is started and begins to travel, the flat spot remains for a period of time before the tire returns to its normal, substantially round shape. During this period, the vehicle could experience sometimes severe vibrations as the flat spot is repeatedly and forcefully brought into contact with the road surface upon which the vehicle is being operated. These vibrations may be harmful to the automobile and uncomfortable for the driver. In order to diminish these deleterious effects, tire manufacturers try to build tires which either form smaller flat spots or return to their round shape as rapidly as possible.
In order to design tires which minimize the adverse effects of the flat spot phenomenon, a method for determining the rate at which the flat spot disappears or decays is needed so that tires can be classified according to their flat spot performance. Currently, a uniformity machine is used to measure the decay of a flat spot on a tire. Unfortunately, a uniformity machine must spin a tire for a short period of time, during which the flat spot decays, before it can measure the initial magnitude of the flat spot and its rate of decay. Thus, a uniformity machine can not accurately measure the magnitude of decay of a flat spot during the initial period of rotation. Therefore, what is needed is an improved method of determining the initial flat spot magnitude and the rate of decay of the flat spot at any given period during tire use.